I have disconnected the 5v and GND from the relay board and I have left the 12v and the GND in the corresponding connectors and the result is the same, the led of the board responds (flashes) but can not activate the relay. I have checked that the 12v arrive at the relay plate.

From the power supply and by means of a steepdown to 7.5v directly Arduino food, by means of another steepdown I give 5v to the clock, sensors, relay module-1, ... and directly 12v to feed the dossing pumps, the surface fans and the power that I carry through the DB25 to the relay module. All the GND are joined in the base PCB that I have built and everything works correctly except the relay module-2 that if it has 12V of voltage measured at the terminals but the only thing I get is that the LEDs are illuminated but not activated the relays.